From the manufacturer

Men's UA Iso-Chill ArmourVent Stretch Hat

This hat was designed to keep your head cool by dumping excess heat through special vents that allow hot air out, but are small enough that the sun's rays aren't an issue.

• Stretch Fit
• ArmourVent Technology delivers ultimate breathability in a light, stretchy, durable & fast-drying fabric
• Material wicks sweat & dries really fast
• Iso-Chill sweatband & front panel lining helps disperse body heat, making it feel cool to the touch
• Stretch construction provides a comfortable fit